The invention relates to a friction pump having pumping surfaces which include areas facing upstream as well as areas facing downstream with respect to the pumping direction.
Molecular pumps and turbomolecular pumps, whose manner of operation is described in detail in the textbook by Wutz, Adam and Walcher entitled "Theorie und Praxis der Vacuumtechnik," pp. 202 sqq., are classed as friction pumps.
In molecular pumps, a moving rotor wall and a stationary stator wall are so configured and spaced apart from one another that the impulses transmitted by the walls to gas molecules situated between them have a preferential direction. As a rule, the rotor wall and/or stator wall are equipped with flute-like indentations or riffles for the achievement of the preferential direction. Molecular pumps operating on this principle are known from German Pat. Nos. 605,902, 625,444, 912,007, 1,010,235 and Swiss Pat. Nos. 101,871, 222,288, as well as from British Pat. No. 332,879.
In recent times turbomolecular pumps have gained favor over molecular pumps. These have intermeshing rows of stator and rotor blades in the manner of a turbine. Different embodiments of turbomolecular pumps are known from Swiss Pat. Nos. 501,840, 529,927, and 564,692, and from German Auslegeschrift No. 1,428,239. By the appropriate arrangement of the stator and rotor vanes it is likewise brought about that more particles are driven in one direction than in the opposite direction.
Lastly, a combination friction pump is known from German Offenlegungsschrift No. 2,412,624. This pump is designed on the suction side as a turbomolecular pump and on the discharge side as a friction pump.
The present invention is addressed to the problem of improving the pumping properties of a friction pump.